Process for production of hydrogen from anaerobically decomposed organic materials

ABSTRACT

A process for the production of hydrogen from anaerobically decomposed organic materials by applying an electric potential to the anaerobically decomposed organic materials, including landfill materials and sewage, to form hydrogen, and for decreasing the time required to treat these anaerobically decomposed organic materials. The organic materials decompose to volatile acids such as acetic acid, which may be hydrolyzed by electric current to form hydrogen. The process may be continuously run in sewage digestion tanks with the continuous feed of sewage, at landfill sites, or at any site having a supply of anaerobically decomposed or decomposable organic materials.

This application is a Continuation-In-Part of patent application Ser.No. 08/659,644 now U.S. Pat. No. 6,090,266.

BACKGROUND OF THE INVENTION

It is recognized that additional sources of energy are needed forsustained industrial growth. There exists an ever present danger independing too heavily on fossil fuels. Fossil fuels (hydrocarbons)represent a limited supply of stored energy which are typically releasedduring a combustion process. By burning hydrocarbons mankind has spewedbillions of tons of toxic pollutants into the atmosphere. It thereforemakes sense from both an environmental and economic standpoint todevelop alternative sources of renewable fuels.

Hydrogen is a fuel which does not produce pollutants, water being itsonly combustion product. Hydrogen has many industrial uses in theproduction of fertilizers, dyes, drugs, plastics, hydrogenated oils andfats and methanol and is used in many industries. It is also used as arocket fuel and in this invention as a minus-emissions fuel that allowsordinary engines to clean the air.

Field of the Invention

This invention relates to a process for the production of hydrogen fromanaerobically decomposed organic materials, including materials such asthose found in landfill materials and sewage sludge, by applying anelectric potential to and thereby creating a current through theanaerobically decomposed organic material and thereby forming hydrogen.

Description of Related Art

The established processes for producing commercially significant amountsof hydrogen are: (1) steam reforming of hydrocarbons, (2) partialoxidation of coal, (3) electrolysis of water, and (4) direct use ofsolar radiation (photovoltaic method).

Steam-reformation of hydrocarbons and partial oxidation of coal aredisadvantageous in that fossil hydrocarbon fuels are consumed.Production of hydrogen by electrolysis of water, a relatively simple andnon-polluting process, is costly and therefore economicallydisadvantageous for most industrial applications because the amount ofenergy needed for electrolysis of water exceeds the energy obtained fromthe combustion of the resulting hydrogen. Photovoltaic methods ofhydrogen production have inherent inadequacy related to access to solarradiation for much of the world's population.

Unlike the methods for production of hydrogen outlined above, theprocess of the present invention does not depend on fossil fuels or thesomewhat random appearance of sunlight to produce hydrogen. The presentprocess converts what are typically waste materials into hydrogen, whilesimultaneously reducing the mass of said materials and/or reducing thetreatment time of such materials by application of a relatively smalland/or intermittent electric potential to said materials. The process ofthis invention uses raw materials typically found in, among otherplaces, municipal waste sites and sewage treatment plants and producesmore energy, in the form of the chemically stored potential energy ofhydrogen, than the electric energy required to produce the hydrogen.

A method of producing hydrogen from sugars is discussed in Energy andthe Environment, Proceedings of the 1st World Renewable Energy Congress,Reading, UK 23-28 Sep. 1990. S. Roychowdhury and D. Cox(“Roychowdhury”). This method involves the production of hydrogen frompure sugars such as glucose or maltose.

Roychowdhury reports the initial production of hydrogen upon inoculationof a sugar solution with so-called “landfill inocula”. To obtainlandfill inocula, materials were obtained from various depths in alandfill, dried, ground (to obtain “landfill powder”) and then incubatedin situ. The incubated culture medium was observed to produce carbondioxide and methane, primarily, and little else, indicating the presenceof highly methanogenic flora in the inoculum. The supernatant from thisculture medium, or in some cases the landfill powder, were used asinocula.

Previously, Roychowdhury disclosed that upon inoculation of varioussugar solutions with the landfill supernatant or landfill powder, thesugar solution produced hydrogen and carbon dioxide, and no methane oroxygen; indicating the presence of hydrogen-producing bacteria presentin the landfill inoculum and/or landfill hydrogen. Hydrogen productiondecreased with increasing acidity.

It is another object of this invention to provide a method of hydrogenproduction which does not require the use of fossil fuels.

It is an object of the invention to serve communities that haverelatively undeveloped electricity distribution and other energyinfrastructures with a system that provides useful energy from collectedwastes.

It is an object of the present invention to separate carbon dioxide,nitrogen and other gases from produced hydrogen.

SUMMARY OF THE INVENTION

This invention relates generally to a process which produces hydrogenfrom anaerobically decomposed organic materials such as anaerobicallycomposted cellulosic materials and anaerobically digested sewage sludge.This process decreases the time required to treat anaerobically composedcellulosic materials and anaerobically digested sewage sludge. Morespecifically, the invention relates to an embodiment wherein arelatively low electric potential is applied to anaerobically decomposedorganic materials such as anaerobically composted cellulosic wastematerials and anaerobically digested sewage sludge which, as a result ofanaerobic decomposition, have been fermented into “volatile” carboxylicacids such as acetic acid and bicarbonates of ammonia. The electriccurrent resulting from the application of an electric potential isbelieved to hydrolyze the acetic acids, other volatile carboxylic acids,and bicarbonates of ammonia within the decomposed materials, therebyproducing hydrogen. Formation of methane is suppressed, Organic mass,such as solids contained within sewage sludge is reduced at an increasedrate, and the time required to treat waste materials such as sewagesludge is thereby reduced.

In another embodiment the time of application of electropotential isintermittent and the duty cycle of voltage application is adaptivelyadjusted to minimize electric power consumption while maximizinghydrogen production. In application it is believed that the activitiesof microorganisms that produce enzymes that release hydrogen from theferment is greatly encouraged and that activities of microorganisms thatproduce enzymes favoring methane production are depressed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow chart showing both production of hydrogen andsuppression of methaneogenesis from anaerobically decomposed organicmaterials in the presence of an applied electropotential, andmethanogenesis from anaerobically decomposed organic materials in theabsence of an applied electropotential.

FIG. 2 is a flow chart showing a process for production of hydrogenwhich includes on-site anaerobic decomposition of organic material.

FIG. 3 is a bar graph representation of the information in Table 1.

FIG. 4 is a bar graph representation of the information in Table 3.

FIG. 5 is a bar graph representation of the information in Table 3.

FIG. 6 is a bar graph representation of the information in Table 5.

FIG. 7 is a bar graph representation of the information in Table 6.

FIG. 8 is a bar graph representation of the information in Table 8.

FIG. 9 is a bar graph representation of the information in Table 9.

FIG. 10 is a bar graph representation of the information in Table 10.

FIG. 11 is a schematic illustration of an embodiment that adaptivelycontrols application of intermittently applied voltage to maximizehydrogen production while minimizing methane production.

FIG. 12 is a schematically illustrated embodiment showing generation ofvoltage for practicing the principles of the invention.

FIG. 13 is a schematic illustrating the principles of another embodimentof the invention.

FIG. 14 is a schematic illustrating the principles of another embodimentof the invention.

DETAILED DESCRIPTION OF THE INVENTION

The process of the present invention may typically be practiced at anylarge municipal landfill or sewage treatment facility, but can bepracticed on a smaller scale wherever anaerobically decomposed organicssuch as anaerobically composted cellulosic materials or anaerobicallydigested sewage sludge are found or may be generated.

Anaerobically composted cellulosic materials are typically found inlandfill materials. Anaerobically digested sewage sludge typicallycomprises sludge found at municipal sewage treatment plants. Landfillmaterials generally consist of approximately 70% cellulosic materialsand have a moisture content of 36% to 46%. Sewage sludge is primarilyliquid, contains volatile acids such as acetic acid, and includes 2-3%solids. Both landfill materials and sewage sludge naturally containmethane-producing abacterial species and hydrogen-producing bacterialspecies.

The invention may be practiced by applying an electric potential ofbetween 1 and 7 volts, preferably between 3 and 6 volts, most preferablybetween 3.0 and 4.5 volts to, and thereby passing an electric currentthrough, anaerobically decomposed organic materials such as landfillmaterials or sewage sludge. This electric potential is applied throughelectrodes which are preferably made from lead, copper, steel, brass orcarbon, more preferably from cast iron bars, and most preferable frommetal impregnated or otherwise electrically conductive graphite.

Anaerobic decomposition, specifically anaerobic composting and anaerobicdigestion, refers to a process where organic compounds, typically butnot limited to compounds of the general formula C_(n)H_(2n)O_(n),decompose in the absence of an oxygen-donor environment. Volatile acidssuch as acetic acid are typically formed by such anaerobicdecomposition. Although anaerobic decomposition may in some instances bepreceded by aerobic decomposition, aerobic decomposition is not aprerequisite to anaerobic decomposition and electrodes can be placedwithin the organic materials prior to the commencement of anaerobicdecomposition.

As described above, both landfill materials comprising anaerobicallycomposted cellulosic materials and anaerobically digested sewage sludgecontain relatively high amounts of volatile acids such as acetic acid.These acids are known to act as electrolytes. In practicing theinvention, one or more sets of electrodes may be placed within landfillmaterial or sewage sludge in such a way that an electric potential isapplied, and according to the principles of the invention resulting inan electrical current with low polarization and ohmic losses. Electrodedistance and placement along with the program of voltage controlincluding occasional reversal of polarity may be adjusted to achievethese conditions. The voltage, average spacing of electrodes and numberof electrodes will vary depending upon the size and composition of thelandfill material or sewage sludge sought to be used to producehydrogen. Electrode sets, may be of any suitable shape, e.g. plates,bars, grids, etc.

In a preferred embodiment of the invention, each individual electrode isplaced into landfill materials and is surrounded by an inert “cage”which effectively ensures that the moisture component of the landfillmaterials, and not a component which might interfere with electricalactivity, is immediately adjacent each electrode. Place of theelectrodes in a suitable position within the landfill material mayrequire some trial and error.

When an electric potential is applied, hydrogen production begins andproduction of hydrogen increases to from 70% to 75% by volume of thetotal gases produced. The level of methane produced decreases from ahigh of approximately 70% by volume of the total gases produced, whenthe electric current is first applied, to greatly diminished tracelevels. Carbon dioxide and nitrogen production remain relativelyconstant and do not vary significantly with methane or hydrogenproduction.

Without being bound by theory, it is believed that the essence of theelectrochemistry of this invention is the enzyme facilitated productionand decomposition of low molecular weight volatile acids such as aceticacid produced by bacterial breakdown of carbohydrates and othernutrients. Because oxygen production is not observed, it is believedthat electrolysis of water is not a source of hydrogen. It is furtherbelieved that hydrogen gas produced by the electrolysis of volatilespresent in the sludge and in landfill materials, inhibits thesubdivision, growth, and activity of methanogenic species.

In a preferred embodiment, cellulosic materials and/or sewage sludge aremade to decompose “on-site”, i.e. in a localized bin or chamber, ratherthan at a centralized landfill or sewage treatment facility. Theanaerobically composted cellulosic waste materials and/or theanaerobically digested sewage sludge are then optionally taken to atransfer station equipped with electrodes as previously described toproduce hydrogen, or alternatively made to produce hydrogen “on-site” byapplication of electric potential at or near the on-site bin or chamber.In this alternate embodiment, hydrogen could then be stored or usedon-sites as a energy source to produce useful forms of energy includingthe relatively minor amount used to practice the principles of theinvention.

Examples Electrodes

Electrodes were cast iron bars, 300 mm long, 25 mm wide and 2.5 mmthick. Other metallic electrodes were used including lead, copper,steel, brass and others. pair of copper impregnated graphite electrodesof the same size was used. Degradation of the graphite electrode was notvery noticeable.

Landfill Materials

Samples of landfill material were obtained from a sanitary landfill atStaten Island N.Y. from a depth of between 30 to 50 feet. The landfillmaterials naturally produce methane and carbon dioxide as primary gases(in 55:35 proportions) through methanogenesis.

Sludge

Sludge samples were taken from a primary digester of a sewage treatmentplant at Brooklyn, N.Y. Sewage sludge produces methane and carbondioxide (in 65:30 proportions) by methanogenesis.

Special Apparatus

A series of experiments were set up to determine whether the productionof hydrogen would take place when voltage was applied through eithersewage sludge or through landfill materials. The pH of the sludge was7.0-7.5 and the pH of the landfill material was 6.5-7.0. Apparatusincluded on 800 ml flask with a three hole rubber stopper. Two of thoseholes were fitted with electrodes and the third hole had a glassdelivery tube. The electrodes and the third hole had a glass deliverytube. The electrodes were connected across two 1.5 volt batteries inseries, resulting in an applied potential of about 3.0 volts. Theapparatus was placed in an incubator set either at 37° C. and later at55° C. Other apparatus included a New Brunswick Fermenter using a 6-8liter glass vessel where the temperature, and rotating stirrer and acooling system could be controlled at a desired setting.

Experimental Data. Example 1

As an experimental control, freshly obtained sewage sludge in an 800 mlflask was placed at 37° C. in an incubator gases, including primarilymethane, were produced as described at Table 1 and depicted at FIG. 3.

TABLE 1 Production of CH₄ and CO₂ DAYS % CH₄ % CO₂ % N₂ 1 65 30 5 2 7025 5 3 70 25 5 4 65 30 4 5 60 35 4 6 55 40 5

Example 2

Sewage sludge from the primary digester was placed in an 800 ml flaskwhich was then placed in a preheated incubator at 37° C. Methane gas wasgenerated. As soon as optimum production of methane was achieved, acurrent was passed through the liquid in the flask. The production ofmethane gas declined gradually and hydrogen and carbon dioxide wereproduced. Methane was completely suppressed when production of hydrogenreached its peak, as described at Table 2 and depicted at FIG. 4.

TABLE 2 Production of H₂ and Suppression of CH₄ DAYS % CH₄ % CO₂ % H₂ 160 35 — 2 70 25 —  3* 45 25 20 4 25 28 46 5  5 30 60 6 TR 30 68 *As andwhen current was passed.

Example 3

Sewage sludge from the primary digester was placed in an 800 ml flaskwhich was then placed in an incubator at 37° C. A current was passedthrough the sludge, applying 3 volts, using the two 1.5 volt batteriesin series. Very little methane was produced at the beginning. Within 3days, production of hydrogen reached its peak and methane gas wasvirtually totally suppressed, as described at Table 3 and depicted atFIG. 5.

TABLE 3 Production of H₂ and CO₂ When Voltage Was Applied From the StartDAYS % H₂ % CO₂ % N₂ % CH₄ 1 65 25 2 8 2 70 25 2 TR 3 70 18 8 TR 4 70 208 — 5 68 25 4 —

Example 4

A sewage sludge sample was placed in a five liter flask in the NewBrunswick Fermenter and 4 electrodes were introduced. Electrical currentwas passed through (2.5 volts and 0.05 to 0.07 Amps). In the beginningonly methane and carbon dioxide were produced with very little hydrogen.As soon as the voltage was increased to 4.0-4.5, and current to0.11-0.15 Amps, methane was gradually suppressed and hydrogen wasproduced as described at Table 4.

TABLE 4 Production of H₂ and CO₂, From Sludge in 5 liter Container DAYS% H₂ % CO₂ % N₂ % CH₄ 1 — 30 12 50 2 5 35 8 46 3 4 30 6 60 5 25 30 5 406 48 25 5 20 7 60 20 2  8 9 70 25 4 TR

Example 5

It is of particular interest to treat landfill materials because thesematerials present municipalities around the world with ubiquitousproblems of vector (rodents, roaches, and communicable disease germs)breeding places along with sources of greenhouse gases and groundwatercontamination due to production of poisonous leachate. The presentinvention provides for carbon sequestration from landfills includingthose that are depositories for sewage sludge.

Landfill materials collected by random borings were provided fordetermination of the least energy expenditures per energy production.Experiments were set up with landfill materials (composted municipalsolid wastes) in two 800 ml flasks, (1) with landfill materials only,(2) with landfill materials where electrodes were dipped in. The resultsare described at Tables 5 and 6, and depicted at FIGS. 6 and 7.

TABLE 5 Production of Gases From Landfill Materials DAYS % H₂ % CO₂ % N₂% CH₄ 1 — — — — 2 — 3 10 — 3 — 20 8 10 5 — 40 6 50 6 — 30 5 63 7 — 30 560 8 — 35 4 60 9 — 35 5 62

TABLE 6 Production of Gases From Landfill Materials in Presence ofApplied Voltage % Total DAYS % H₂ % CO₂ % N₂ CH₄ CC 1 53 — All — 95 2 728 13 — 302 3 76 17 6 — 500 4 75 18 6 — 600 5 72 18 6 — 450 7 79 18 6 —600 9 65 18 14 — 500

Example 6

Example 5 was repeated: (1) with sludge only, (2) with sludge havingoperating electrodes. The results are described at Tables 7 and 8, anddepicted FIG. 8.

TABLE 7 Production of Gases From Sludge in Absence of Applied Voltage %DAYS % H₂ % CO₂ % N₂ CH₄ Total CC 2 — 20 14 65 50 3 — 14 10 70 125 4 —19 4 72 225 5 — 22 4 66 258 6 — 18 8 70 200

TABLE 8 Production of Gases From Sludge in Presence of Applied Voltage %DAYS % H₂ % CO₂ % N₂ CH₄ Total CC 2 65 28 4 8 85 3 70 20 2 TR 200 4 7018 8 TR 310 5 70 20 2 — 330 6 68 22 4 — 258

Example 7

An experiment was set up with landfill materials in a 6 liter vesselwith electrodes. A current was created through the landfill materials byapplying an electric potential of 3.5 V. The results are described atTable 9 and depicted at FIG. 9.

TABLE 9 Production of Gases From Landfill Materials in 6 Liter VesselWith Applied Voltage DAYS % H₂ % CO₂ % N₂ % CH₄ TOTAL 1 75 TR 12 — 100 270 5 10 — 1020 4 75 7 15 — 850 6 75 8 17 — 750 8 70 5 20 — 600

Example 8

Landfill materials in a 6 liter vessel were placed in a preheatedincubator at 55° C. After 4 days electrodes were connected to 3.5 voltterminals. The results are described at Table 10, and depicted at FIG.10.

Similar results are achieved by mixing a relatively small amount ofinoculum of human sewage sludge with farm manure and/or crop wastes.After an incubation period in which anaerobic conditions wereestablished, methane and carbon dioxide were produced with very littlehydrogen. Upon presentation of voltage at 2.0 to 5.0 volts to causecurrent to reach 0.10 to 0.20 Amps, methane production was depressed andhydrogen was again produced as summarized in Table 10. Similar resultsare achieved by use of inoculum from previous runs of Example 4 andprovide improvements in the efficiency of conversion of chemical energypotential of organic substances 25 into hydrogen.

TABLE 10 Production of Gas from landfill Materials in Two DifferentEnvironments In the Same Set-Up DAYS % H₂ % CO₂ % N₂ % CH₄ TOTAL 1 — 5All — 20 2 — 20 35 125 3 — 35 55 200 4  5* — 30 20 150 7 25 31  7 150 860 35 TR 250 9 68 31 — 285 10  65 30 — 200

FIG. 11 shows an embodiment 200 in which suitable electrodes such asconcentric electrodes 202 and 204 receive intermittently applied voltageto influence the solvated organic waste between the electrodes toproduce hydrogen more or less according to the data shown in Tables 8,9, and 10. In operation, voltage is applied by voltage source 216according to a duty cycle controlled by relay 212 that is constantlyadjusted by controller 210 to facilitate hydrogen generation and toprevent substantial methane production.

Feedback information from gas detector 206/208 is provided to controller210. If trace amounts of methane are detected a voltage is appliedbetween electrodes 202 and 204 for a recorded time period until methaneproduction is depressed. The time until methane traces are detectedagain is noted by controller 210 and a duty cycle of applying voltageacross electrodes 202 and 204 for a time interval slightly longer thanthe time noted for depressing methane production followed by neutralelectrode operation for a time period slightly less than the time notedpreviously for traces of methane to be detected.

This duty cycle is adaptively changed to shorten the time of voltageapplication and to extend the time between voltage application forpurposes of minimizing methane production while maximizing hydrogenproduction with least application of voltage to electrodes 202 and 204.Voltage level is reduced to provide another variable and adaptivelyadjusted with respect to the time of voltage application to minimizeenergy expenditure. This adaptive control algorithm rapidly adjusts forchanges in organic waste composition, moisture content, temperature, andother variables.

FIG. 12 shows an embodiment in which the fuel gas produced by theprocess of the invention in the presence of electrodes 230 and 232 is inpart made available for energy conversion in 240 to electricity by afuel cell or engine-generator set. Adaptively controlled application ofvoltage to electrodes 230 and 232 is provided by controller 236 andrelay 234 as shown for purposes of minimizing energy consumption pertherm of hydrogen produced.

Moreover, adaptive controller 236 provides a control algorithm tominimize methane production while facilitating maximum hydrogenproduction. Solenoid operated valve 238 controls delivery of fuel gas byline 242 to energy conversion unit 240 as needed to meet adaptivelyadjusted duty cycle and to meet other demands for electricity asdelivered by insulated cables 244. Suitable power for pumping water,providing a heat-pump cycle, or production of electricity at 240 may beby a heat engine and generator, a fuel cell, a thermoelectric generator,or other devices that convert fuel potential energy into electricity.

In many applications, it is preferred to utilize a piston engine andgenerator in which the engine is fueled with a SmartPlug combinationfuel injector and ignition system to facilitate extremely robustoperation. SmartPlug operation is disclosed in U.S. Pat. Nos. 5,394,852and 5,343,699. This enables the raw mixture of hydrogen and carbondioxide to be used as a very low grade fuel without further conditioningwhile producing very high thermal efficiency and full rated power incomparison with engine operation on gasoline or diesel fuel. This is aparticularly important advantage for remote operation and to bring fueland power to depressed economies where it is prohibitive to importfossil-based fuels.

Preferential production of hydrogen provides thermodynamic advantagesbased on faster fuel combustion, wider air/fuel ratio combustion limits,and with SmartPlug operation the engine operates essentially withoutthrottle losses. These thermodynamic advantages provide much higherbrake mean effective pressure or “BMEP” for the same heat release incomparisons with gasoline or diesel fuel.

As shown in Table 11, it is possible to actually clean the air with anengine generator running on hydrogen-characterized fuel produced fromlandfill or sewage organic wastes. The ambient air was cleaned byoperation of an engine that is compared in operation between hydrogenand gasoline.

TABLE 11 TEST RESULTS AMBIENT 29 ppm HC 0.00 ppm CO 1.0 ppm NO AIR TEST:(hydrocarbons) (Carbon Monoxide) (Nitrogen Monoxide) ENGINE WITHHYDROGEN OPERATION Idle: 18 ppm HC 0.00 ppm CO 1.0 ppm NO Full Power: 6ppm HC 0.00 ppm CO 2.0 ppm NO USING GASOLINE AS FUEL IN THE SAME ENGINE:Idle: 190 ppm HC 25,000 ppm CO 390 ppm NO Full Power: 196 ppm HC 7,000ppm CO 95 ppm NO

Substantial amounts of carbon dioxide are produced along with hydrogenby operation of electro-conditioned anaerobic digestion of organicwastes. Economical separation of hydrogen from the carbon dioxide isneeded for fuel cell applications, for increasing the storage density ofhydrogen, and for increasing the value of hydrogen produced. Suchseparation is provided by the embodiment of FIG. 13. This embodimentalso serves the purpose of providing for utilization 25 of the carbondioxide for various purposes including use in greenhouses or hydroponicsand is an important aspect of the invention.

The solubility of carbon dioxide in water is about 21.6 volumes of gasper volume of water at 25 atmospheres pressure and 12° C. (54° F.).Increasing the pressure or decreasing the temperature increases theamount of carbon dioxide dissolved per volume of water. Lowering thepressure or increasing the temperature releases dissolved carbondioxide. In most areas of the Earth, the ground water is maintained at atemperature that is equal to the mean annual air temperature plus onedegree (F.) for each 80′ of overburden to the saturated zone.

FIG. 13 shows a system for separating carbon dioxide from hydrogen bydifferential absorption of carbon dioxide within a suitable medium suchas water or a hindered amine. In operation, mixed gases consisting ofhydrogen, carbon dioxide, and lesser amounts of nitrogen and other gasesare forced into the bottom of a column of water 302 approximately 1,000′or higher.

It is generally preferred to use a column of water that is developed byplacing a well approximately 1000′ below the saturated zone of the localgroundwater. This provides the extremely large heat sink benefit of thesub soil including the ground water in the saturated zone where thetemperature is generally constant at the desired temperature of 4° C. to16° C. (40° F. to 60° F.) for most climate zones throughout the year.Water columns that are elevated along mountain slopes are also feasiblebut may suffer freezing conditions in the winter and unfavorable warmingin the summer season.

Mixed gases are delivered to the bottom of tube 304 by a suitable pump(not shown). Mixed gases enter into a suitable scrubber zone such as thehelical fin 306 that is attached to tube 304 with a higher elevation atthe point of attachment than any other point on the element of rotationthat describes the helical surface as shown. Gases thus tend to bebuoyed towards tube 304 as they are scrubbed by the absorbing fluid.Carbon dioxide readily enters into solution at the pressure andtemperature conditions maintained. Hydrogen exits at the top of thehelix into tube 308 and is delivered to the surface for various uses.

Carbon-dioxide rich water is ducted to the surface by coaxial tube 310as shown. As the head pressure lessens, carbon dioxide bubbles developand escape upward and create a lower density mixture that is buoyantlylifted to the gas separator section 312 where denser water 25 that haslost the ability to retain carbon dioxide is returned to annular space302 and sinks the bottom to replace the upward travelling inventory ofwater that is lifted within tube 310. Carbon dioxide is collected at thetop of 310 by tube 314 for various useful purposes.

FIG. 14 shows an embodiment in which energy used to pressurize thehydrogen and carbon dioxide is regeneratively recovered by an expansionengine. Embodiment 400 shows an extremely rugged and simple energyconversion system that combines various renewable resources such assewage, garbage, and farm wastes with solar energy to supplyelectricity, hydrogen, and carbon dioxide.

In many situations and applications it is preferred to pressurize waterin a suitable vessel 402 to provide for the separation by solubilitydifferences as desired to purify hydrogen. In operation, mixtures ofhydrogen and carbon dioxide are forced through tube 404 into pressurevessel 402 at the nominal pressure of 450 PSI. It is preferred toutilize a spiral mixer consisting of a helical fin 406 that causes themixture of gases to scrub along the surface and form highsurface-to-volume ratios. The mixed gases follow an extended paththrough the water as carbon dioxide is absorbed to allow the hydrogen tobe collected at the top of spiral scrubber 406 by tube 408 as shown.Carbon dioxide is absorbed into the water while hydrogen is collected atthe top of separator 406 as shown.

Hydrogen is delivered by conduit 408 for immediate use in an engine orfuel cell or it may be stored for future use as needed. Carbon dioxidesaturated water is taken from absorber vessel 402 by tube 410 to valvemanifold 426 which provides control valves to time the flow of carbondioxide rich water into each of a group of heat exchangers such as 414,416, 418, 420, 422, and 424 as shown. Each heat exchanger is providedwith an exit a nozzle that is aimed at the blades or buckets of anadjacent fluid motor rotor such as 430, 432, 434, 436, 438, and 440which deliver work to a common output shaft as shown.

An inventory of water and carbon dioxide solution under pressure issuddenly forced into a preheated heat exchanger such as 414 by brieflyopening the control valve that serves 414. As the fluid is heated thetemperature and pressure of the fluid increases and it vaporizes and isexpelled with very high momentum to power motor 430. Each of the otherheat exchanger chambers receives a charge of fluid on a timed basis sothat the shaft power from the group of motors shown can be considered tohave multiple phase torquing such as six phase if each heat exchangerreceives flow at a different times or three phase if two heat exchangersare filled simultaneously. A suitable application of the output of thefluid motor is generator 428 or other useful loads as needed.

It is preferred to provide concentrated radiation to the heat exchangersby a suitable solar collector such as a field of heliostats or aparabolic dish 442 as shown. At times that solar energy is insufficientto meet energy conversion needs, supplemental heat may be applied bycombustion from a suitable burner 448. For such supplemental heating itis preferred to use mixtures of carbon dioxide and hydrogen and/or othercombustible gases released by anaerobic digestion of organic matter.

After undergoing heating and expansion to a suitably low pressure,carbon dioxide is collected by tube 458 and taken to a suitableapplication. Water is condensed and collected in reservoir 450 which iscooled by countercurrent heat exchanger 456 by circulation of a suitableheat exchange fluid from 446 to 456 and then through 448 to a suitablecogeneration application. Cooled water is pressurized by pump 454 andreturned to pressure vessel 402 to complete the novel carbon dioxideremoval and energy conversion cycle.

SUMMARY OF THE INVENTION

Method and apparatus for utilization of intermittently applied voltagefor depression of methane production while maximizing hydrogengeneration from organic landfill and sewage wastes is provided alongwith a rational control regime for minimizing the energy expenditure todo so. Renewable biomass and solar resources are combined in a uniqueenergy conversion regime. Production of electricity from an engineoperated on hydrogen sourced by the invention is integrated in asynergistic combination that provides regenerative separation of carbondioxide from fuel gas air and cleaning with carbon sequestration.

The time to dispose of organic materials is preferably reduced byanaerobically digesting such materials in a reaction zone and applyingart electric potential across the zone thereby producing hydrogen andcarbon dioxide. It is preferred to apply the electric potentialoccasionally after periods without application of said electricpotential. It is preferred to apply the electric potential at afrequency and for a period to maximize the quantity of hydrogen producedper the amount of electricity consumed.

It is preferred to separate carbon dioxide and fuel produced bypressurizing a fluid to a state that provides preferential absorption ofcarbon dioxide, mixing the fuel and carbon dioxide with the pressurizedfluid, and collecting the fuel that remains after preferentialabsorption of carbon dioxide. Energy conversion efficiency is increasedby adding heat to the fluid after preferential absorption of carbondioxide for the purpose of increasing the amount of work produced by amotor that expands the pressurized fluid, releasing the carbon dioxidein conjunction with the expanding process, and cooling the fluid beforethe pressurizing step.

The preferred source of such heat is selected from the group includingsolar energy, heat released by combustion of a portion of the fuelproduced, concentrated solar energy, and a combination of solar energyalong with heat produced by combustion of a portion of the hydrogen.

An energy conversion process is provided by the steps of anaerobicallydigesting organic materials to produce carbon dioxide and fuel selectedfrom the group including hydrogen, methane, and mixtures of hydrogen andmethane, separating the carbon dioxide from the fuel. The preferredmethod of separation is comprised of pressurizing a fluid to a statethat provides preferential absorption of carbon dioxide, mixing thecarbon dioxide and fuel with the fluid, collecting the fuel that remainsafter said preferential absorption of carbon dioxide, adding heat to thefluid after preferential absorption of carbon dioxide for the purpose ofincreasing the amount of work produced by a motor that expandspressurized fluid, releasing carbon dioxide in conjunction with theexpanding process, and cooling the fluid before the pressurizing step.

In instances that it is preferred to utilize anaerobic digestion toproduce hydrogen instead of methane, feedstock organic materials areplaced in a reaction zone and an electric potential or voltage isapplied across the materials thereby producing hydrogen and carbondioxide. It is preferred to provide application of intermittent voltagefor purposes selected from the group including depression ofmicroorganismal activity that produces methane, enhancement ofmicroorganismal activity that produces hydrogen, and creation of anatmosphere within organic materials that is maintained rich in hydrogen.The process intermittent application of voltage is optimized by feedbackinformation from a gas detector as provided to a controller means. Iftrace amounts of methane are detected, the voltage is applied for arecorded time period until methane production is depressed, the timeuntil methane traces are detected again is noted by the controller and aduty cycle is provided for applying voltage for a time interval slightlylonger than the time noted for depressing methane production followed byneutral electrode operation for a time period slightly less than thetime noted previously for traces of methane to be detected in thisprocess, the voltage level is variably reduced to provide an adaptivelyadjusted control with respect to the time of said voltage application tominimize energy expenditure.

1-22. (canceled)
 23. A process for producing hydrogen from anaerobicallydigested organic materials comprising the steps of: placing saidmaterials in a reaction zone; and applying an electric potential acrosssaid materials; thereby producing hydrogen and carbon dioxide wherebysaid electric potential is applied occasionally after periods withoutapplication of said electric potential.
 24. A process as in claim 23 inwhich said occasional application of said electric potential is timed tooccur at a frequency and for a period to maximize the quantity ofhydrogen produced per the amount of electricity consumed.
 25. A processas in claim 23 wherein a portion of said hydrogen is used by an energyconversion means to supply said electric potential.
 26. A process as inclaim 23 in which said occasional application of said electric potentialis timed to occur at a frequency and for a period to maximize thequantity of hydrogen produced per the amount of electricity consumed andwherein a portion of said hydrogen is used by an energy conversion meansto supply said electric potential.
 27. A process as in claim 23 in whichsaid electric potential is applied across electrodes.
 28. A process asin claim 23 in which said electric potential is applied across multipleelectrodes.
 29. A process for producing hydrogen from anaerobicallydigested organic materials comprising the steps of: placing saidmaterials in a reaction zone; and applying an electric potential acrosssaid materials; thereby producing hydrogen and carbon dioxide wherebysaid electric potential is applied occasionally after periods withoutapplication of said electric potential whereby the amount of timerequired to reduce the amount of said organic materials is substantiallyreduced compared to the time required without application of saidelectric potential.
 30. A process for conversion of biomass wastes intouseful energy comprising the steps of: application of intermittentvoltage for purposes selected from the group including depression ofmicroorganismal activity that produces methane, enhancement ofmicroorganismal activity that produces hydrogen, and creation of anatmosphere within said biomass wastes that is maintained rich inhydrogen.
 31. The process of claim 30 in which said voltage is generatedby means selected from the group including: an hydrogen fuel cell, anengine using hydrogen for fuel, a combination of a fuel cell and anengine both using hydrogen fuel, and a thermoelectric generator.
 32. Theprocess of claim 30 in which an inoculum means selected from the groupincluding human sewage, medium from mature anaerobic digestion oforganic materials within an occasionally applied voltage, and mediumfrom anaerobic digestion that is conducted in the presence of increasedconcentrations of hydrogen wherein said inoculum is added tosubstantially organic materials selected from the group includingmanure, crop wastes, and garbage for purposes of increasing theefficiency of conversion of chemical potential energy in organicmaterials to hydrogen.